Conventional aeronautical structures have typically been made for decades with metal materials such as aluminium, stainless steel or titanium. Thus, the protection of these conventional aeronautical structures against lightning strikes has been based on the good electrical continuity inherent to said metal materials.
Aeronautical structures are currently increasingly made in composite materials, such as carbon fiber, since these materials provide the configured structures with a low specific weight. However, composite materials do not have a good electrical continuity, whereby it is necessary to provide them with a special structure so that the aeronautical structures that they form are protected against lightning strikes. In the event of not having these configurations, when a structure of composite materials is struck by a lightning, hot spots and/or possible electric arcs are generated, this being critical in the event that it is a fuel tank.
One of the known solutions consists of performing a metallization of the structures manufactured in composite materials, one or several foils or meshes of metal materials, such as aluminium, copper or bronze, being used to that end, said foils or meshes being adhered during the process for manufacturing the aeronautical structures (typically panels) to the outer face therefore, which will receive the direct lightning strike.
Current technology ensures a good, and at the same time robust, integration of the mentioned outer metal layer with the assembly of composite material, typically carbon fiber. This metalization ensures a good protection of the structure and maximizes the conduction of the electric charge discharged by the strike towards the discharge (“exit”) devices to the atmosphere. However, the efficiency of this metalization solution is reduced during the drilling process of the aeronautical structures (particularly panels), this drilling is necessary to connect the structures or panels to other components of the structures, such as ribs, spars or stringers. Thus, the drilling of the panels and their subsequent countersinking ensures that the head of the rivets/fasteners does not create an aerodynamic protrusion, but it breaks the outer metalization (foils or meshes), and a dielectric contact is being created between the head of the rivet and the countersinking. This will not ensure a good electrical contact between the head of the rivets and the “metallization” layers, meshes or foils. This gives rise to increasing the energy that is passed to the internal structure through bolt, rivet.
Various processes are known for re-establishing the good electrical continuity between the head of the rivet and the metallized structure (meshes or foils). One of the most used solutions consists of using special washers ensuring the contact between the head of the rivet and the metallization mesh of the structures or panels, although they have problems of weight, of increase of the aerodynamic drag of the structure as the profile thereof is not continuous, while at the same time the assembly of said washers increases the manufacturing time, furthermore basing the protection against lightning on an element which can be lost or forgotten during the assembly or maintenance of the aircraft.
The present invention offers a solution to the aforementioned problems.